Bad breath is a combination of many oral diseases or systemic diseases. Patients with bad breath are affected to some extent in their daily life and psychologically. Bad breath can be caused by local causes: such as poor oral hygiene, not paying attention to brushing and rinsing after meals; long-term smoking; accumulation of dental calculus, bacterial plaque and soft scale on the tooth surface, especially in the neck of the teeth and the interdental space; filling of food residues in cavities of teeth or corrosion of carious dentin, etc., which produces bad odor due to chemical decomposition, i.e. bad breath. Other diseases in the mouth such as oral ulcers, osteomyelitis of the jaw, maxillary sinusitis, tonsillitis, thick tongue, etc., can also make the mouth exhale unpleasant odor. Bad breath may also be related to the following factors: 1, respiratory system diseases: chronic paranasal sinusitis, bronchial ulcer disease, bronchiectasis, lung abscess, etc., can be in the exhaled gas with bad odor. 2, digestive system diseases: esophageal lesions, gastric ulcers or digestive tract cancer, etc., can cause normal digestive dysfunction, resulting in indigestion, producing odor gas through the esophagus by the oral elimination. 3, metabolic diseases: such as diabetic patients with ketosis can be discharged from the mouth rotten apple odor. 4, chemical poisoning: long-term contact with certain metals, phosphorus, arsenic, bismuth and other poisoning, from the oral cavity can be emitted like the smell of garlic. 5, pharmaceutical factors: long-term use of certain drugs, from the oral cavity can be emitted from the smell of drugs. 6, improper brushing method: such as horizontal brushing not only can not clean the food residue and dirt between the teeth, but because of too much force is also easy to squeeze the tooth surface soft dirt, food residue, etc. into the gap, corrosion and fermentation in the oral cavity, resulting in bad breath odor. The correct method is to choose a toothbrush suitable for their mouth size, up and down back and forth along the long axis of the teeth vertical line pick brush, a little force can be. 7, oral dryness: for some reason the oral saliva secretion is too little; or long speech, nasal congestion mouth breathing and other factors may produce bad breath. Rich saliva is a natural mouthwash. To deal with simple oral dryness caused by bad breath, the method is very simple, as long as more water can be eliminated. However, with the growth of age oral saliva secretion will gradually reduce, so the elderly need to drink more water. 8, some dietary structure and habits will also produce bad breath: eat too much onion, garlic, onions, leeks, etc.; long-term drinking, smoking and other oral cavity will also have bad odor. These odors, bad breath can take some measures to deal with, such as timely brushing teeth after meals, rinse mouth. If the occasion conditions are restricted, you can drink more water especially more tea is a good way, in addition, chewing tea, chewing gum can also be eaten to cover up bad breath. Especially tea can help remove dirt from the surface of the teeth and eliminate odor. Mouthwash with fresh scent can cover bad breath. In addition, you can eat some fruits such as apples after eating garlic can remove the smell of garlic. Because apples are hard foods, they rub the surface of the teeth when chewing and play a role in cleaning the teeth, which can clean the food residue on the surface of the teeth. Most of the symptoms of bad breath are caused by local causes. If the cause cannot be found after detailed examination of the local oral cavity and careful questioning of relevant habits, further examination should be conducted in internal medicine or related specialties to clarify the cause and target treatment.